This invention relates to electric hammers, and in particular to demolition hammers.
Such hammers will normally contain a housing and a spindle that extends through an aperture in the housing at the front end of the hammer. The hammer is normally provided with an impact mechanism comprising a motor that drives a reciprocating piston in the spindle, which in turn drives a ram and a beat piece in the spindle by means of an air cushion mechanism. Such mechanisms are well known and will not be described further. The spindle allows insertion of the shank of a bit, for example a drill bit or a chisel bit, into the front end thereof so that it is retained in the front end of the spindle with a degree of axial movement, and is, in operation of the hammer, repeatedly struck by the beat piece.
It is possible for some hammers to be employed in combination impact and drilling mode in which the spindle, and hence the bit inserted therein, will be caused to rotate at the same time as the bit is struck by the beat piece, but most hammers will be able to be employed in pure impact mode or so-called xe2x80x9cchippingxe2x80x9d mode (whether or not they can also be employed in other modes) in which the bit is struck by the beat piece without rotation of the spindle. In this mode, the hammer will usually be employed with a flat chisel bit rather than with a generally cylindrical drill bit, and it will often be desired by the operator of the hammer to change the orientation of the chisel bit in the hammer to adjust to different positions and/or orientations of the surface that is being worked on. Thus a number of arrangements have been proposed for enabling the bit to be rotated with respect to the hammer during use. It will be appreciated that the orientation of the spindle itself needs to be changed when the orientation of the bit is changed since the bit will usually be capable of being coupled in the spindle at one or two orientations only.
A number of designs of hammer have been proposed in which the orientation of the bit in the spindle may be changed. However, such designs have normally suffered from the disadvantage that the hammer includes a spindle locking mechanism that is actuated by moving a part axially along the spindle, before the spindle is rotated to its desired position. The operation of changing the orientation of the bit thus becomes rather awkward, requiring the operator to move the tool holder in one direction and then maintain the tool holder in that position while rotating it. Furthermore, the spindle locking mechanism will usually require a relatively strong bias against movement in the axial direction since it is in the axial direction of the spindle that the hammer is subject to impacts during normal operation, and the mechanism must withstand such impacts. Thus, it would be desirable for a hammer to employ a spindle locking mechanism that can be actuated by rotation only.
According to one aspect, the invention provides a hammer which comprises:
a housing having an aperture therein;
a spindle that is located in the housing, and extends out of the housing through the aperture, the spindle being capable of being rotated about its axis to any of a plurality of orientations; and
a locking ring that is located around the spindle and which can be moved axially along the spindle at least to a limited extent into and out of engagement with the aperture of the housing, but cannot rotate about the spindle, so that when the locking ring engages the aperture, it prevents the spindle from rotating with respect to the housing; and
the hammer additionally comprises a grip ring that is located around the spindle and can be rotated by the operator of the hammer about the axis of the spindle from a normal operating position in which it prevents disengagement of the locking ring from the aperture in the housing to a second position in which the locking ring is disengaged from the aperture of the housing, thereby to allow the spindle to rotate with respect to the housing to a different orientation.
Thus, it is possible to form a hammer in which the orientation of the bit can be changed in a particularly simple manner: the operator simply rotates the grip ring to a position in which the spindle lock is released, or at least can be released, and then rotates the grip ring further, which may, if desired, be against a slightly higher resistance to rotation, until the bit is in the correct orientation. Preferably the grip ring is biased to the normal operating position at which disengagement of the locking ring from the aperture is prevented. In a preferred embodiment the grip ring will move under its bias to the normal operating position when it is released by the operator, so that no further operation is necessary once the bit is in the correct position. In a preferred embodiment, rotation of the grip ring to the second position causes part of the grip ring to bear on the locking ring in the circumferential direction so that further rotation of the grip ring beyond the second position will cause it to rotate the locking ring and thereby the spindle.
As stated above, the locking ring cannot rotate about the spindle (and thus is able to lock the spindle in its orientation in the aperture). It is capable of being rotated about the axis of the spindle, and will be rotated in this manner when the orientation of the tool bit is changed, but when it is rotated about the axis of the spindle it will cause the spindle itself to be rotated. This may be achieved by a number of means, essentially by ensuring that the mating parts of the spindle and locking ring do not have circular cross-sections. For example, the spindle may be provided with flats on its periphery, or it may have a polygonal, e.g. hexagonal, cross-section, or it may have a number of axially extending splines, and, whatever form of spindle, the bore of the locking ring will have a complementary shape. Like the locking ring, the grip ring can also be rotated about the axis of the spindle. However, in some forms of the hammer, the grip ring can be rotated about the spindle, at least to a limited extent, that is to say, it can be rotated about the axis of the spindle at least to a limited extent without the spindle itself rotating. In one form of hammer, rotation of the grip ring to the second position causes a part of the grip ring to bear on the locking ring in the circumferential direction so that further rotation of the grip ring beyond the second position will cause it to rotate the locking ring and thereby the spindle, since the locking ring cannot rotate about the spindle. This may be achieved if one of the locking ring and the grip ring has at least one protuberance that extends in the axial direction into an aperture or recess in the other of the locking ring and the grip ring. In this case, the aperture or recess may extend in the circumferential direction to a greater extent than the protuberance to allow the grip ring to be rotated to the second position without rotation of the locking ring, but to allow rotation of the grip ring beyond the second position only with rotation of the locking ring.
The locking ring and the grip ring may be so configured that at least part of the grip ring will abut the locking ring in the axial direction and maintain it in engagement with the aperture in the normal operating position, but when the grip ring has been rotated to a certain extent, the abutting parts move away from one another to allow axial movement of the locking ring, either freely or against a bias applied to the locking ring. This may be achieved, for example by means of one or more axial protuberances on one of the locking ring and the grip ring that bear on part of the other of the locking ring and the grip ring, but which will move circumferentially out of the way when the grip ring is rotated. In this way, the grip ring may be rotated about the spindle from the normal operating position in which it holds the locking ring in engagement with the housing aperture and thereby locks the spindle in one position with respect to the hammer, to the second position (without so far any rotation of the locking ring) in which the locking ring is still in engagement with the aperture, but is not held in engagement with the aperture by the grip ring. Further rotation of the grip ring about the spindle will cause the locking ring, and hence the spindle, to rotate. In order to do this, the locking ring must move out of engagement with the aperture. This may be achieved by providing at least one of the locking ring and the housing with at least one surface that is bevelled (in the circumferential direction in relation to the axis of the spindle) and bears on part of the other of the locking ring and the housing so that the bevelled surface forces the locking ring out of engagement with the aperture when it is rotated about the axis of the spindle by the grip ring. Preferably the locking ring and the aperture each have bevelled surfaces that bear on one another to force the locking ring out of engagement with the aperture. Such bevelled surfaces may, for example, be formed on teeth that are provided on the locking ring and on the housing aperture and which engage one another in the normal operating position.
In another form of hammer, the locking ring may be urged into engagement with the aperture by some means other than the grip ring, such as a spring, and a screw mechanism is provided so that rotation of the grip ring will move the locking ring axially along the spindle out of engagement with the aperture. In this form of hammer, the grip ring and the locking ring may be provided with at least one surface that bears on a corresponding surface of the other of the grip ring and the locking ring and which is bevelled in the circumferential direction in relation to the axis of the spindle, i.e. has a helically extending portion, so that the surface forces the locking ring out of engagement with the aperture when the grip ring is rotated to the second position.
The grip ring may be biased into its normal operating position by any of a number of means. For example, one or more springs may be provided that extend in the circumferential direction between parts of her grip ring and the locking ring. Alternatively, a bias ring may be provided that is located around the spindle and is biased axially toward the grip ring, at least one of the grip ring and the bias ring having at least one surface that bears on the other of the grip ring and the bias ring in the axial direction and slopes in such a direction that the grip ring is biased to its normal operating position.
Often, the grip ring will be arranged so that it will not be able to move axially along the spindle, and this requirement may be necessary when the grip ring prevents, in normal use, the locking ring from sliding axially along the spindle in a forward direction. However, this is not essential, and in some forms of hammer, limited axial movement of the grip ring along the spindle may be allowed (although this is not normally advantageous). For example, it is normally necessary to provide some means for limiting axial movement of the grip ring along the spindle toward the aperture, in order to enable the grip ring to move the locking ring along the spindle out of engagement with the aperture. However, if some means other than the grip ring is used to keep the locking ring in engagement with the aperture in normal use, it is possible to allow some forward movement of the grip ring.
While the spindle locking mechanism will often be provided as an integral part of a hammer, and especially of a hammer that is designed to be employed only in chipping mode, it is possible for the mechanism to form part of a tool holder that can be removed from the remainder of the hammer. Thus, according to another aspect, the invention provides a tool holder for attachment to a hammer which comprises:
a housing part having an aperture therein;
a spindle that is located in the housing part, and extends out of the housing part through the aperture, the spindle being capable of being rotated about its axis to any of a plurality of orientations;
a locking ring that is located around the spindle and which can be moved axially along the spindle at least to a limited extend into and out of engagement with the aperture of the housing part, but cannot rotate about the spindle, so that when the locking ring engages the aperture, it prevents the spindle from rotating with respect to the housing part; and
the hammer additionally comprises a grip ring that is located around the spindle and can be rotated by the operator of the hammer about the axis of the spindle from a normal operating position in which it prevents disengagement of the locking ring from the aperture in the housing part to a second position in which the locking ring is disengaged from the aperture of the housing part, thereby to allow the spindle to rotate with respect to the housing to a different orientation.